1. Field of the Invention
The present invention relates generally to buffered switches. More particularly, the present invention relates to deferred queuing in a buffered switch to alleviate head of line blocking in the buffered switch.
2. Description of the Related Art
Communication switches are often used in information networks to transfer information between devices within the network. These switches can have as few as four ports or as many as thousands of ports. Each input port generally requires some amount of buffer space to store frames or packets of information prior to the frames or packets being forwarded to an output port.
One problem associated with buffered switches is head of line blocking Head of line blocking occurs in switches that have a single receive buffer at each ingress port. When multiple packets or frames of data are queued up (in line) for transmission through a central switch and the destination of the packets or frame at the front of the queue (head of line) is not available for reception, the queue is defined as “head of line blocked.” This is because, not only is that packet or frame blocked, all packets or frames behind the blocked packet or frame in the queue are blocked even though their destination may be available. Thus, all packets or frames are blocked until the packet or frame at the head of the queue is transmitted.
One way to solve head of line blocking is to provide one receive buffer at each of the switch's ingress ports for every egress port. For small switches, this approach may be feasible. However for very large switches, massive amounts of memory must be used to provide buffering for all of the outputs. If the switch requires a large input buffer due to long haul applications, the problem is exacerbated further. Accordingly, it is desirable to provide a method and apparatus for alleviating the problems associated with head of line blocking in a buffered switch without using separate buffers for every output.